1. Field of the Invention
This invention relates to a drive unit which can perform recording and reproduction of data on a recording medium.
2. Description of the Related Art
Operations which read, decode and perform error correction on written information are carried out not only during normal reproduction from a recording medium such as a magneto-optic disk, but also at the time of so-called write-and-verify.
Write-and-verify is an operation which reads recorded data immediately after a recording operation, and checks whether the data was recorded correctly.
However, when information is read and decoded during reproduction and verification, errors may occur which are impossible to correct.
In such a case, a retry operation, such as re-reading a sector where the error occurred (a sector being a data unit on a disk, described later), is performed.
However, if an error occurs during decoding, an operation is performed before starting the read retry which checks whether data recording on the sector is complete (hereafter, referred to as xe2x80x9cwrittenxe2x80x9d status) or whether data recording has not taken place (hereafter, referred to as xe2x80x9cblankxe2x80x9d status).
This is because the causes of decoding errors such as ECC errors and the retry methods that should be performed depend on the written/blank status of the sector.
For example, if the sector is blank when a read error occurs during write-and-verify, there is a strong possibility that not the read-operation, but the write operation was not perfomed correctly. On the other hand, if the sector is blank when a read error occurs during normal reproduction, an error will naturally occur and a read retry operation is unnecessary.
In order to make such a determination, a validation (hereafter, referred to as xe2x80x9cblank checkxe2x80x9d) of the written/blank status of a sector is required. However, since a read had to be repeated on the sector where the error occurred to perform this blank check, it was necessary to wait for the time of at least one disk rotation after the error occurred. This delayed the start of the retry action, and as a result, the information reading speed of the drive unit decreased.
Due to the need to perform a blank check, to retry reading a certain sector once, two reads (two accesses of the sector by the head) are required, i.e., one read for the blank check and one read for the retry). Consequently the time required for one retry operation was long, and the upper limit on the number of retries that could be made was used up. For example, if an error re-occurs when a retry read is performed, another retry has to be performed, but since there is an upper limit to the number of retries that can be made, it will be impossible to read the data if it cannot be successfully decoded by the time this upper limit is reached. The upper limit is set considering the time required to make retries, and it a long time is required for one retry, the upper limit will have to be set to a low number. However if the upper limit is low, the probability of a successful read by retry will fall, and this will limit the reading performance of the drive unit.
It is therefore an object of this invention to perform suitable retries rapidly in a short time.
For this purpose, the drive unit of this invention comprises a head means which reads information from a recording medium, a decoding means which performs decoding and error correction corresponding to a modulation scheme on information read by the head means, an identifying means which identifies whether this information comes from a written area or a blank area on the recording medium when the information read by the head means is decoded by the decoding means, and a control means which checks the identification result from the identifying means and performs a retry operation according to this identification result when an error occurs during decoding by the decoding means.
In other words, a blank check is performed simultaneously by the identifying means when the read data is decoded, and if a decoding error occurs, a suitable retry action is rapidly begun by immediately identifying the blank check status.
According to this invention, it the identification result from the identifying means is a blank area, decoding by the decoding means is stopped. In other words, in the case of a blank area, error correction is not performed needlessly.